I just said that everything is ok, than I updated Symbiostock to 2.5.6 and got again white screen.....Help!
Did you do anything else after Leo got it working (install plugins, update plugins, etc)?
I know it's too late now... but anytime someone plans on updating a plugin or theme or anything else, they should always take a backup. This way if something breaks, they can "roll back". The good news is that your site is kind of still in "beta". So problems at this point don't affect sales or customers getting annoyed and never returning.